MADRID - Pope Benedict XVI urged more than 1.5 million young people to become missionaries for the faith Sunday, giving them words of encouragement as he concluded a glitch-marred church youth festival and announced that the next edition will be in Rio de Janeiro in 2013.

Benedict told the pilgrims at a Madrid airfield hosting World Youth Day that they should not keep their faith private but participate fully in the life of their parishes and remain in communion with the church.

"So do not keep Christ to yourselves! Share with others the joy of your faith," he said. Hours earlier, a fierce thunderstorm during a prayer vigil at the airfield had forced Benedict to cut short his remarks and slightly injured six people when a tent collapsed. Some makeshift chapels set up on the field's perimeter were also damaged, forcing organizers to announce Sunday morning over loudspeakers that not everyone would be able to receive Communion during the Mass.

In fact, Yago de la Cierva, head of the World Youth Day organizing committee, said almost none of the young people received the Eucharist during the Sunday Mass, a serious letdown for such fervent Catholics to be denied the sacrament.

Despite the discomfort and disappointment, pilgrims who spent the night in sleeping bags, tents and under tarps seemed unfazed as they awoke to sunny skies Sunday. Organizers announced they were opening a new area at the base to accommodate late arrivals.

"The night was amazing, I didn't sleep at all," said Adrinna Wista, a 21-year-old Polish pilgrim. "We stayed the night chatting, meeting new people and praying with them. Amazing."

Cristina Velasquez, a 29-year-old from Venezuela, said she spent the night with a group of Indian pilgrims after police, who had initially told her the airfield was full, let her in as the rain came down.

"Sleeping was difficult because the ground is quite stony. But waking up was indescribable, we are all so happy and united," she said. "The pope's words have made me proud to be making this sacrifice for his and Christ's sake."

Neither police nor the regional government have provided an official crowd count, but Vatican spokesman the Rev. Federico Lombardi said it was entirely "credible" that more than 1.5 million people took part.

Benedict arrived at the field Sunday morning and processed through the crowd in his white popemobile to the cheers and chants of the flag-waving pilgrims. Spain's King Juan Carlos and Queen Sofia were on hand.

In his initial remarks to the crowd, Benedict said he hoped the young people had managed to get some sleep despite the weather. On Saturday, 2,500 had been treated for mostly heat-related problems amid temperatures that soared to 40C (104F), organizers said.

The 84-year-old pontiff was kept comfortable during Sunday's Mass by a cooling system erected on the altar; a steady mist blew down on him from a golden treelike structure shading the altar, which was set against a long undulating white backdrop.

This is Benedict's third World Youth Day, the gathering of young Catholics from around the world once every three years that was launched a quarter-century ago by Pope John Paul II in a bid to reinvigorate and spread the faith among the young. It has the feel of a weeklong rock concert and camping trip, with bands of flag-toting pilgrims roaming through Madrid's otherwise empty streets to take part in prayer and education sessions, Masses, cultural outings and papal events.

At the end of Sunday's Mass, Benedict officially announced that the next World Youth Day will take place in Rio in 2013 - a year early to avoid conflicts with the 2014 World Cup in Brazil - and said he hoped to attend. Brazilians in the crowd jumped, whooped and cheered at the announcement.

"I think this is great for Brazil and its youth because it's a very Catholic country," said Brazilian pilgrim Rogerio Moreira, 35. "It's a very good experience for those who can't attend other World Youth Days."

At a wrap-up briefing, Lombardi said the pope was pleased with he event despite the difficulties the storm threw his way.

"Life is made up of unforeseen things, of confronting something new and not just following a program that is carried out perfectly like we might have hoped," Lombardi said. The pope's decision to stick out the storm "I think was a beautiful test, a beautiful demonstration of patience, even courage and commitment to carry forward his witness."

But Lombardi too couldn't hide his disappointment that so many observant Catholics were denied the crucial sacrament during the Mass.

De La Cierva explained that the tent-chapels had been sealed by police as a safety precaution after the storm damaged some; the Eucharistic hosts were sealed inside them as well.

De la Cierva also acknowledged some other glitches: some people who had credentials to be at the field were turned away Saturday because some non-credentialed pilgrims had taken their places; in addition, some pilgrims broke out of the barriers dividing the field into quadrants and occupied the spaces reserved for emergency vehicles, preventing Benedict from being able to process through in his popemobile Saturday night as planned.

"The Holy Father, with great pain, had to cancel," the procession, de la Cierva said. "This for us was a real shame, to not let the people see the Holy Father." The quadrants were re-established by Sunday morning.